Lens for 400D (XTi)

I read at various places that good lens can improve the results of camera.
Which lens is recommended for amature photography that will work with 400D (XTi) ?
I expect a sharp lens.
My experience of film photography with EOS300 is that SIGMA is sharper than Tamron.

Brands a Brand. Sigma and Tamron are both reasonably good brands nowadays. Some of their lenses even compare to Canon and Nikon lenses and outperform them image quality wise, although it seems build quality is better on the cheaper Nikons and Canons than the cheaper Sigmas and Tamrons.

All brands have good lenses and bad lenses. Technical reviews on lenses can be found at www.photozone.de to compare the sharpness CA vignetting and distortion. Then it comes down to what you are shooting. Obviously the best lenses are primes (fixed in focal length). They offer professional results for very good prices. Professional zooms that are f/2.8 over their entire zoom range on the other hand cost a mint.

If you tell us what you like to photograph and a rough budget I'm sure the guys and girls here can recommend several good lenses.

Thanks Garbz for the reply.
I have set aside about $2000 for this project.
400D costs with 18-55 kit lens $950, without kit $890
D30 costs $1450 with 18-55 kit lens.
I own temeron Aspherical XR (IF) A03 of my EOS 300 (film) :er: not sure what can I do with that.
Not decided as to what shall I shoot, but I am bit exiced to shoot whatever I see.
I am in the desert of middle east so I guess I have mostly dunes and desert around to shoot. I can shoot tall buildings etc. Can do some abstract photography. I am on the coast with 2 minute drive to sea.
Another question : is it really useful to have prime lens ?
ketan

Good glass is worth the investment because it will hold its value really well. Check the buy/sell section and you will notice that L glass if its in really good condition will sell for most likely 90%-95% of its original value.

Mike had a great list of lenses and I personally am eying up a couple of those for the future. I would add to it the 50mm f/1.8 by Canon. Its only around $75 (cheapest lens they make) and optically is pretty good.

Don't make that sad face .
Sigma has also great lenses in the catalogue, 30mm F1,4 DC EX is my favourite lens and the 17-70mm F2,8-4,5 DC Macro is more than often screwed on the 30D. 18-50mm F2,8 DC EX Macro is also a nice one.

You can browse my photos searching for lenses. That may give you an idea, assuming that theses shoots could have been made with a 400D, you would not notice any difference.